Symmetric coalescence of two hydraulic fractures

Abstract

<p id="d5586833e195">We present an experimental investigation on the coalescence of hydraulic fractures in a brittle solid. Using a dual-fracturing setup, we obtain high-resolution experimental measurements on the time evolution of the fracture profiles and internal velocity field before, during, and after fracture coalescence. These measurements show an intermediate time self-similar coalescence during the dynamic interaction of two fractures. The work probes the dynamic formation of a fracture network, which is crucial to the industrial practice of energy resource recovery, compensation grouting, and the reservoir integrity of many confined systems involving fluid injection. </p><p class="first" id="d5586833e198">The formation of a fracture network is a key process for many geophysical and industrial practices from energy resource recovery to induced seismic management. We focus on the initial stage of a fracture network formation using experiments on the symmetric coalescence of two equal coplanar, fluid-driven, penny-shaped fractures in a brittle elastic medium. Initially, the fractures propagate independently of each other. The fractures then begin to interact and coalesce, forming a bridge between them. Within an intermediate period after the initial contact, most of the fracture growth is localized along this bridge, perpendicular to the line connecting the injection sources. Using light attenuation and particle image velocimetry to measure both the fracture aperture and velocity field, we characterize the growth of this bridge. We model this behavior using a geometric volume conservation argument dependent on the symmetry of the interaction, with a 2D approximation for the bridge. We also verify experimentally the scaling for the bridge growth and the shape of the thickness profile along the bridge. The influence of elasticity and toughness of the solid, injection rate of the fluid, and initial location of the fractures are captured by our scaling. </p>